With reference to FIG. 1, a gas chromatograph is typically comprised of: (a) a supply of a carrier gas 20; (b) a carrier gas flow controller 22, (c) a sample injection port 24 that allows a sample of unknown or uncertain composition to be injected into a stream of the carrier gas, (d) a separation column 26 for receiving a carrier gas and a sample borne by the carrier gas, (e) an oven 28 for heating a sample being borne by a carrier gas and passing through the separation column, (e) a detector 30 for identifying one or more components of the sample, (f) a recorder 32 for recording the results produced by the detector, and (g) a controller 34 for coordinating the operation of other elements of the gas chromatograph, including the temperature profile to which a sample that is passing through the separation column is subjected.
The separation column is a long, tubular structure that has the desired size exclusion, chemical affinity, or other characteristic or combination of characteristics that cause the structure to provide different degrees of retention to the various chemical analytes as they are pushed along the column and towards the detector. The tubular separation column is typically comprised of three sections—an inlet section that initially receives the carrier gas and sample, a wound section that receives the carrier gas and sample from the inlet section and constitutes the bulk of the length of the column, and an outlet section that receives the carrier gas and sample from the helically wound section. The wound section typically is in the form of a circular helix. Typically, the ends of the column associated with the inlet and outlet sections each have a coupling element that allows the column to be attached to and detached from the carrier gas circuit. This allows columns with different characteristics to be used in the chromatograph.
A typical oven for use in gas chromatography is comprised of: (a) a housing that defines an interior chamber, (b) a heating element located in the chamber and that is used to heat the air in the chamber, the heated air then being used to heat a sample that is passing through a separation column located in the interior chamber, (c) a fan blade that is located in the interior chamber and used to circulate the heated air, (d) a device for positioning a separation column in the interior chamber, (e) a vent system for use in regulating the passage of air into and out of the interior chamber to facilitate a desired air temperature within the interior chamber, and (f) a temperature sensor for sensing the air temperature within the interior chamber. The housing is typically made of sheet metal, with the surface of the sheet metal defining the interior chamber, and a thick inorganic blanket that covers all or a substantial portion of the sheet metal and operates to deter heat transfer from the oven to the ambient atmosphere. Since the separation column for use in the analysis of one sample may not be appropriate for the analysis of another sample, the housing typically incorporates a door that allows a separation column located in the oven to be removed and replaced with another separation column. The vent system operates to prevent ambient air from entering the chamber when the air in the chamber is being heated and allow ambient air into the chamber when cooler air in the chamber is desired.